On 12 Dec, 20:58, Ed Sirett wrote:
Start with the simple stuff first, has someone inadvertently moved the
heating *temperature setting on the boiler?

There are dozens of possibilities. Make and model will eliminate a number
of them.

It's a WB HighFlow 400 (an infamous combi if my googling is right).
I've given the diverter valve a bash tonight and it's not helped it
unjam and I can't see any obvious way on this boiler to force it to
open the CH flow. One I did notice is that the temperature of the the
rads is not constant: some are warmer than others and a couple and
cold at the bottom and warmish at the top.

Jon